Activated TAFI Promotes the Development of Chronic Thromboembolic Pulmonary Hypertension: A Possible Novel Therapeutic Target.

RATIONALE: Pulmonary hypertension is a fatal disease; however, its pathogenesis still remains to be elucidated. Thrombin-activatable fibrinolysis inhibitor (TAFI) is synthesized by the liver and inhibits fibrinolysis. Plasma TAFI levels are significantly increased in chronic thromboembolic pulmonary hypertension (CTEPH) patients. OBJECTIVE: To determine the role of activated TAFI (TAFIa) in the development of CTEPH. METHODS AND RESULTS: Immunostaining showed that TAFI and its binding partner thrombomodulin (TM) were highly expressed in the pulmonary arteries (PAs) and thrombus in patients with CTEPH. Moreover, plasma levels of TAFIa were increased 10-fold in CTEPH patients compared with controls. In mice, chronic hypoxia caused a 25-fold increase in plasma levels of TAFIa with increased plasma levels of thrombin and TM, which led to thrombus formation in PA, vascular remodeling, and pulmonary hypertension. Consistently, plasma clot lysis time was positively correlated with plasma TAFIa levels in mice. Additionally, overexpression of TAFIa caused organized thrombus with multiple obstruction of PA flow and reduced survival rate under hypoxia in mice. Bone marrow transplantation showed that circulating plasma TAFI from the liver, not in the bone marrow, was activated locally in PA endothelial cells through interactions with thrombin and TM. Mechanistic experiments demonstrated that TAFIa increased PA endothelial permeability, smooth muscle cell proliferation, and monocyte/macrophage activation. Importantly, TAFIa inhibitor and peroxisome proliferator-activated receptor-α agonists significantly reduced TAFIa and ameliorated animal models of pulmonary hypertension in mice and rats. CONCLUSIONS: These results indicate that TAFIa could be a novel biomarker and realistic therapeutic target of CTEPH.

A direct oral anticoagulant edoxaban accelerated fibrinolysis via enhancement of plasmin generation in human plasma: dependent on thrombin-activatable fibrinolysis inhibitor.

A direct oral anticoagulant, edoxaban, is as effective as vitamin K antagonists for the treatment of venous thromboembolism (VTE). However, the mechanism underlying the treatment effect on VTE remains to be determined. The aims of this study were to evaluate the effect of edoxaban on tissue plasminogen activator (t-PA)-induced clot lysis in human plasma and to determine the roles of plasmin and thrombin-activatable fibrinolysis inhibitor (TAFI) in the profibrinolytic effect by edoxaban. Pooled human normal plasma or TAFI-deficient plasma (containing 180 ng/mL t-PA and 0.1 nM thrombomodulin) was mixed with edoxaban or an activated TAFI inhibitor, potato tuber carboxypeptidase inhibitor (PCI). Clot was induced by adding tissue factor and phospholipids. Clot lysis time and plasma plasmin-α2 antiplasmin complex (PAP) concentration were determined. Clot structure was imaged with a scanning electron microscope. In normal plasma, edoxaban at clinically relevant concentrations (75, 150, and 300 ng/mL) and PCI significantly shortened clot lysis time. PCI increased PAP concentration and a correlation between PAP concentration and percent of clot lysis was observed. Edoxaban also dose-dependently elevated PAP concentration. In TAFI-deficient plasma, the effects of edoxaban and PCI on clot lysis and PAP concentration were markedly diminished as compared with normal plasma. Fibrin fibers were thinner in clots formed in the presence of edoxaban. In conclusion, edoxaban at clinically relevant concentrations accelerates t-PA-induced fibrinolysis via increasing plasmin generation in human plasma. The effects of edoxaban is mainly dependent on TAFI. The profibrinolytic effect of edoxaban might contribute to the efficacy for the treatment of VTE.

Thrombin-activatable fibrinolysis inhibitor protects against acute lung injury by inhibiting the complement system.

Acute lung injury (ALI) is a devastating disease with an overall mortality rate of 30 to 40%. The coagulation/fibrinolysis system is implicated in the pathogenesis of ALI. Thrombin-activatable fibronolysis inhibitor (TAFI) is an important component of the fibrinolysis system. Recent studies have shown that the active form of TAFI can also regulate inflammatory responses by its ability to inhibit complement C3a, C5a, and osteopontin. We hypothesized that TAFI might have a protective role in ALI. To demonstrate this hypothesis, the development of ALI was compared between wild-type (WT) and TAFI-deficient mice. ALI was induced by intratracheal instillation of LPS. Control mice were treated with saline. Animals were killed 24 hours after LPS. The number of inflammatory cells and the concentration of total protein and inflammatory cytokines were significantly increased in bronchoalveolar lavage fluid from LPS-treated, TAFI-deficient mice compared with their WT counterparts. Significantly higher concentrations of C5a were found in bronchoalveolar lavage fluid and plasma in LPS-treated TAFI knockout mice compared with WT mice. Pretreatment with inhaled C5a receptor antagonist blocked the detrimental effects of TAFI deficiency to levels found in WT mice. Our results show that TAFI protects against ALI, at least in part, by inhibiting the complement system.

Role of thrombin-activatable fibrinolysis inhibitor in allergic bronchial asthma.

BACKGROUND: Bronchial asthma is an inflammatory disease of the airways. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase that besides inhibiting fibrinolysis, also regulates inflammatory processes. The only validated substrate known for TAFI is fibrin. In the present study we evaluated the role of TAFI in bronchial asthma by comparing the development of allergic bronchial asthma between wild-type (WT) and TAFI-deficient mice (KO). METHODS: Asthmatic inflammation was induced by sensitization and challenge with ovalbumin in WT (WT/OVA) and TAFI KO (KO/OVA) mice. WT mice (WT/SAL) and TAFI KO (KO/SAL) were used as controls. Cytokines, markers of inflammation, and coagulation were measured in bronchoalveolar lavage fluid (BALF). RESULTS: Airway hyperresponsiveness was worse in KO/OVA mice than in WT/OVA mice or control mice. Markers of lung injury were significantly increased in BALF from KO/OVA mice compared to WT/OVA mice. Airway hyperresponsiveness and the BALF concentrations of IL-5 and osteopontin were significantly increased in KO/OVA mice compared to WT/OVA mice. Treatment of WT/OVA and KO/OVA mice with a C5a receptor antagonist significantly decreased hyperresponsiveness along with the BALF concentrations of total protein and C5a compared to untreated asthmatic mice. CONCLUSION: The results of this study suggest that TAFI plays a protective role in the pathogenesis of allergic inflammation probably by inhibiting the complement system.

Enhanced abdominal aortic aneurysm formation in thrombin-activatable procarboxypeptidase B-deficient mice.

OBJECTIVE: To determine whether procarboxypeptidase B (pCPB)(-/-) mice are susceptible to accelerated abdominal aortic aneurysm (AAA) development secondary to unregulated OPN-mediated mural inflammation in the absence of CPB inhibition. METHODS AND RESULTS: Thrombin/thrombomodulin cleaves thrombin-activatable pCPB or thrombin-activatable fibrinolysis inhibitor, activating CPB, which inhibits the generation of plasmin and inactivates proinflammatory mediators (complement C5a and thrombin-cleaved osteopontin [OPN]). Apolipoprotein E(-/-)OPN(-/-) mice are protected from experimental AAA formation. Murine AAAs were created via intra-aortic porcine pancreatic elastase (PPE) infusion. Increased mortality secondary to AAA rupture was observed in pCPB(-/-) mice at the standard PPE dose. At reduced doses of PPE, pCPB(-/-) mice developed larger AAAs than wild-type controls (1.01+/-0.27 versus 0.68+/-0.05 mm; P=0.02 [mean+/-SD]). C5(-/-) and OPN(-/-) mice were not protected against AAA development. Treatment with tranexamic acid inhibited plasmin generation and abrogated enhanced AAA progression in pCPB(-/-) mice. CONCLUSIONS: This study establishes the role of CPB in experimental AAA disease, indicating that CPB has a broad anti-inflammatory role in vivo. Enhanced AAA formation in the PPE model is the result of increased plasmin generation, not unregulated C5a- or OPN-mediated mural inflammation.

Procarboxypeptidase R deficiency causes increased lethality in concanavalin A-induced hepatitis in female mice.

Carboxypeptidase R (CPR), also known as thrombin-activatable fibrinolysis inhibitor (TAFI), is an enzyme generated by proteolytic cleavage of its zymogen (proCPR). CPR removes the C-terminal arginine from inflammatory peptides such as C3a and C5a, bradykinin, enkephalin, and the thrombin-cleaved N-terminal fragment osteopontin (cleaved N-OPN). In the mouse model of concanavalin A (Con A)-induced immune-mediated fulminating hepatitis, cleaved N-OPN is one of the important peptides that induce the production of chemokines or cytokines. In the current study using proCPR deficient mice, we showed that injection of Con A into the mouse tail vein can induce a significantly higher lethality in proCPR-deficient female but not in male mice. Furthermore, a lack of CPR activity increased serum macrophage inflammatory protein-2 (MIP-2) and high-mobility group box 1 (HMGB1) levels after Con A injection. These in vivo findings suggest that CPR helps to protect against Con A-induced hepatitis.

Protective role of thrombin activatable fibrinolysis inhibitor in obstructive nephropathy-associated tubulointerstitial fibrosis.

BACKGROUND: Thrombin-activatable fibrinolysis inhibitor (TAFI) has been reported to affect wound healing and fibrotic processes, but its role in renal tubulointerstitial fibrosis remains unknown. OBJECTIVE: To study its potential role, we compared TAFI-deficient and wild-type mice for the degree of renal fibrosis caused by unilateral ureteral obstruction (UUO). METHODS: The grade of tubulointerstitial fibrosis, the activity of plasmin, MMP-2 and MMP-9 were evaluated on days 4 and 9 after UUO. RESULTS: The renal content of hydroxyproline and the activity of plasmin, MMP-2 and MMP-9 were significantly increased in kidneys with UUO from TAFI-deficient mice compared with those from wild-type mice. These differences disappeared when animals with UUO from both groups were treated with the plasmin inhibitor tranexamic acid. The renal concentrations of fibrogenic cytokines were also significantly elevated in kidneys with UUO from TAFI-deficient mice compared with those from wild-type mice. CONCLUSION: The results of this study suggest that increased renal activity of plasmin in TAFI-deficient mice causes increased renal interstitial fibrosis in obstructive nephropathy.

Immune complex-mediated glomerulonephritis is ameliorated by thrombin-activatable fibrinolysis inhibitor deficiency.

The activity of plasmin plays a critical role in the development of chronic glomerulonephritis. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a potent inhibitor of plasmin generation. We hypothesized that TAFI is involved in the pathogenesis of glomerulonephritis because it inhibits plasmin generation. To demonstrate this hypothesis, we compared the development of immune complex-mediated glomerulonephritis in wild-type and TAFI-deficient mice. After six weeks of treatment with horse spleen apoferritin and lipoplysaccharide to induce glomerulonephritis, mice deficient in TAFI had significantly better renal function as shown by lower concentrations of albumin in urine and blood urea nitrogen compared to wild-type mice. In addition, the activity of plasmin and matrix metalloproteinases was significantly increased, and mesangial matrix expansion and the deposition of collagen and fibrin in kidney tissues were significantly decreased in TAFI-knockout mice as compared to their wild-type counterparts. Depletion of fibrinogen by batroxobin (Defibrase) treatment led to equalization of the renal function and the amount of collagen deposition in the kidneys of TAFI-knockout and wild-type mice with immune complex-mediated glomerulonephritis. Together these observations suggest that TAFI-mediated inhibition of plasmin generation plays a role in the pathogenesis of glomerulonephritis, and that it may constitute a novel molecular target for the therapy of this disease.

TAFI deficiency in liver cirrhosis: relation with plasma fibrinolysis and survival.

INTRODUCTION: TAFI (thrombin-activatable fibrinolysis inhibitor) is a potent anti-fibrinolytic and anti-inflammatory factor of liver origin. It is markedly reduced in liver cirrhosis but its effect on fibrinolysis remains controversial and no data are available on its prognostic value. We evaluated the relationship of TAFI level with plasma fibrinolysis and survival in cirrhotic patients. PATIENTS AND METHODS: Sixty-five patients with liver cirrhosis were studied. TAFI antigen, plasma fibrinolysis and other laboratory variables were assayed at study entry and their association with mortality was assessed during a 3-year follow-up. RESULTS: TAFI level and fibrinolysis time were markedly reduced in liver cirrhosis as compared to healthy subjects (p<0.0001) and TAFI deficiency was strongly correlated with fibrinolysis time (p=0.0002). TAFI level at entry, but not fibrinolysis time, was significantly lower in non-survivors (n=25) than in survivors (n=40, p=0.0001). By Cox regression analysis, after adjustment for possible confounding factors, TAFI, but not fibrinolysis time, was identified as an independent predictor of mortality. TAFI assay, moreover, showed a clinically relevant accuracy in assessing patients' survival (ROC curve analysis, p<0.0001) achieving a sensitivity of 92%, a specificity of 55%, and a negative predictive value of 91.7%. CONCLUSIONS: Our data indicate that TAFI deficiency in liver cirrhosis is associated with enhanced plasma fibrinolysis. Moreover, they suggest that TAFI, but not fibrinolysis time, is a strong predictor of survival and thus TAFI assay might prove useful to select candidates for liver transplantation.

Carboxypeptidase B2 and N play different roles in regulation of activated complements C3a and C5a in mice.

Essentials Two basic carboxypeptidases are present in plasma, B2 (CPB2) and N (CPN). Cpb2-/- and Cpn-/- mice were challenged in a hemolytic uremic syndrome (HUS) model vs. wild type. Cpb2-/- exacerbates HUS while Cpn-/- exacerbates cobra venom factor challenge vs. wild type mice. CPB2 and CPN have overlapping but non-redundant roles. SUMMARY: Background There are two basic carboxypeptidases in plasma. Carboxypeptidase B2 (CPB2) is activated from a circulating zymogen, proCPB2, and carboxypeptidase N (CPN) is constitutively active with both inactivating complement C3a and C5a. Aims To test the roles of CPB2 and CPN in complement-driven mouse models of cobra venom factor (CVF) challenge and hemolytic-uremic syndrome (HUS). Methods Cpb2-/- , Cpn-/- and wild-type (WT) mice were compared in an HUS model induced by Shiga toxin and lipopolysaccharide administration and following CVF administration. Results HUS was exacerbated in Cpb2-/- mice more than in Cpn-/- mice, compared with WT mice. Cpb2-/- mice developed the HUS clinical triad of microangiopathic hemolytic anemia, uremia and thrombocytopenia. Treatment with anti-C5 antibody improved survival of both Cpb2-/- and Cpn-/- mice. In contrast, when challenged acutely with CVF, the reverse phenotype was observed. Cpn-/- mice had markedly worse disease than Cpb2-/- mice, whereas the WT mice were resistant. Conclusions CPN and CPB2 play overlapping but non-redundant roles in regulating complement activation in vivo. The constitutively active CPN is key for inactivation of systemic C5a, whereas CPB2 functions as an on-demand supplementary anaphylatoxin inhibitor in inactivating excessive C5a formed locally.

Thrombin-activatable fibrinolysis inhibitor (TAFI) deficiency is compatible with murine life.

To investigate the consequence of deficiency in thrombin-activatable fibrinolysis inhibitor (TAFI), we generated homozygous TAFI-deficient mice by targeted gene disruption. Intercrossing of heterozygous TAFI mice produced offspring in the expected Mendelian ratio, indicating that transmission of the mutant TAFI allele did not lead to embryonic lethality. TAFI-deficient mice developed normally, reached adulthood, and were fertile. No gross physical abnormalities were observed up to 24 months of age. Hematological analysis of TAFI-deficient mice did not show any major differences including plasma fibrinogen level, prothrombin time, and activated partial thromboplastin time. TAFI-deficient mice did not suffer from excess bleeding as determined by blood loss following tail transection, although their plasma failed to prolong clot lysis time in vitro. In vivo, TAFI deficiency did not influence occlusion time in either an arterial or a venous injury model. TAFI deficiency did not improve survival rate compared with the wild-type in thrombin-induced thromboembolism, factor X coagulant protein-induced thrombosis, and endotoxin-induced disseminated intravascular coagulation. Furthermore, TAFI deficiency did not alter kaolin-induced writhing response, implying that TAFI does not play a major role in bradykinin catabolism. The current study demonstrates that TAFI deficiency does not change normal responses to acute challenges.

[The TAFI system. The new role of fibrinolysis]. / Das TAFI-System. Die neue Rolle der Fibrinolyse.

The primary focus of the blood coagulation system is the prevention of blood loss. The system is regulated by various inhibitors, and by the fibrinolytic system, which removes the final product of the blood coagulation system, the fibrin clot. The fibrinolytic system is activated in the course of coagulation activation. The thrombin-activated fibrinolysis inhibitor (TAFI) is an important regulator of fibrinolysis. TAFI is activated by thrombin, and activation is enhanced in the presence of thrombomodulin. TAFIa, the product of TAFI activation, removes lysine residues from fibrin, which are essential for the binding of t-PA, plasminogen, and plasmin to fibrin. The fibrin loses its cofactor activity in t-PA-induced plasminogen activation, resulting in less plasmin, and the remaining plasmin finds less binding sites on fibrin, resulting in an increased resistance of the clot towards plasmin proteolysis. High concentrations of thrombin result in high TAFIa-activity and consequently in highly resistant fibrin clots. Patients with hyperprothrombinaemia consequently display elevated TAFIa-levels, which may contribute to the risk for thrombosis. Treatment with recombinant factor VIIa also leads to high concentrations of thrombin, resulting in fibrin clots with enhanced resistance towards fibrinolysis. At low thrombin concentration, as observed in patients with bleeding disorders or patients treated with anticoagulant drugs, less TAFIa is produced in the course of coagulation activation, and the clots are less resistant towards fibrinolysis. TAFIa-inhibitors are currently being developed for the treatment of throboembolic disorders or hypofibrinolytic DIC. Enhancement of TAFIa-activity may be helpful in patients with bleeding.

Demonstration of enhanced endogenous fibrinolysis in thrombin activatable fibrinolysis inhibitor-deficient mice.

To investigate the importance of thrombin activatable fibrinolysis inhibitor (TAFI) in the stabilization of plasma clots, we have compared fibrinolysis in TAFI-deficient (KO) and wild-type (WT) littermate mice. TAFI-deficient mice were previously generated by targeted gene disruption. The level of TAFI activity generated in plasma from WT mice in the presence of added thrombin and thrombomodulin (activatable TAFI) is twice that of plasma from TAFI heterozygous mice (HET); no activatable TAFI is detected in TAFI KO plasma. In vitro, TAFI KO plasma clots lysed faster than WT plasma clots, and HET plasma clots lysed at an intermediate rate. The rate of clot lysis for KO mice is not changed in the presence of potato carboxypeptidase inhibitor, a specific inhibitor of TAFIa, whereas the WT and HET clot lysis rates are increased in the presence of potato carboxypeptidase inhibitor. C-terminal lysine residues are preserved on partially degraded clots from KO mice, but are absent from partially degraded WT clots. In vivo, in a batroxobin-induced pulmonary embolism model, KO mice displayed a lower retention of fibrin in the lungs than did WT mice. These results are the first demonstration of enhanced endogenous fibrinolysis in an in vivo model without the addition of exogenous thrombolytic.

Thrombin-activatable fibrinolysis inhibitor influences disease severity in humans and mice with pneumococcal meningitis.

BACKGROUND: Mortality and morbidity in patients with bacterial meningitis result from the proinflammatory response and dysregulation of coagulation and fibrinolysis. Thrombin-activatable fibrinolysis inhibitor (TAFI) is activated by free thrombin or thrombin in complex with thrombomodulin, and plays an antifibrinolytic role during fibrin clot degradation, but also has an anti-inflammatory role by inactivating proinflammatory mediators, such as complement activation products. OBJECTIVE: To assess the role of TAFI in pneumococcal meningitis. METHODS: We performed a prospective nationwide genetic association study in patients with bacterial meningitis, determined TAFI and complement levels in cerebrospinal fluid (CSF), and assessed the function of TAFI in a pneumococcal meningitis mouse model by using Cpb2 (TAFI) knockout mice. RESULTS: Polymorphisms (reference sequences: rs1926447 and rs3742264) in the CPB2 gene, coding for TAFI, were related to the development of systemic complications in patients with pneumococcal meningitis. Higher protein levels of TAFI in CSF were significantly associated with CSF complement levels (C3a, iC3b, and C5b-9) and with more systemic complications in patients with bacterial meningitis. The risk allele of rs1926447 (TT) was associated with higher levels of TAFI in CSF. In the murine model, consistent with the human data, Cpb2-deficient mice had decreased disease severity, as reflected by lower mortality, and attenuated cytokine levels and bacterial outgrowth in the systemic compartment during disease, without differences in the brain compartment, as compared with wild-type mice. CONCLUSIONS: These findings suggest that TAFI plays an important role during pneumococcal meningitis, which is likely to be mediated through inhibition of the complement system, and influences the occurrence of systemic complications and inflammation.

Carboxypeptidase B2 deficiency reveals opposite effects of complement C3a and C5a in a murine polymicrobial sepsis model.

BACKGROUND AND OBJECTIVES: Carboxypeptidase B2 (CPB2) is a basic carboxypeptidase with fibrin and complement C3a and C5a as physiological substrates. We hypothesized that in polymicrobial sepsis, CPB2-deficient mice would have sustained C5a activity, leading to disease exacerbation. METHODS: Polymicrobial sepsis was induced by cecal ligation and puncture (CLP). RESULTS: Contrary to our hypothesis, Cpb2(-/-) mice had significantly improved survival, with reduced lung edema, less liver and kidney damage, and less disseminated intravascular coagulation. Hepatic pro-CPB2 was induced by CLP, leading to increased pro-CPB2 levels. Thrombomodulin present on mesothelium supported thrombin activation of pro-CPB2. Both wild-type and Cpb2(-/-) animals treated with a C5a receptor antagonist had improved survival, demonstrating that C5a was detrimental in this model. Treatment with a fibrinolysis inhibitor, tranexamic acid, caused a decrease in survival in both genotypes; however, the Cpb2(-/-) animals retained their survival advantage. Administration of a C3a receptor antagonist exacerbated the disease in both wild-type and Cpb2(-/-) mice and eliminated the survival advantage of Cpb2(-/-) mice. C5a receptor is expressed in both peritoneal macrophages and neutrophils; in contrast, C3a receptor expression is restricted to peritoneal macrophages, and C3a induced signaling in macrophages but not neutrophils. CONCLUSIONS: While C5a exacerbates the peritonitis, resulting in a deleterious generalized inflammatory state, C3a activation of peritoneal macrophages may limit the initial infection following CLP, thereby playing a diametrically opposing protective role in this polymicrobial sepsis model.

Tumor growth and metastasis are not affected in thrombin-activatable fibrinolysis inhibitor-deficient mice.

Many studies have indicated that the plasminogen activation system may have a prominent role in cancer. Activation of the zymogen plasminogen into the serine protease plasmin by plasminogen activator is mediated by carboxyterminal basic amino acids in fibrin, including lysines and arginines. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating carboxypeptidase B-type proenzyme that, after activation, removes carboxyterminal lysine or arginine residues in fibrin, resulting in decreased plasminogen activation and attenuated fibrinolysis. To determine directly whether TAFI is involved in primary tumor growth and metastasis formation, we examined the effects of TAFI deficiency on subcutaneous growth and experimentally or spontaneously induced pulmonary metastasis formation of different tumor cell types in mice. In all tumor models TAFI deficiency did not affect the formation and growth of primary and metastasized tumors.

Low levels of thrombin activatable fibrinolysis inhibitor (TAFI) in patients with chronic liver disease.

Thrombin Activatable Fibrinolysis Inhibitor (TAFI) is a 60 kappaD glycoprotein present in plasma that regulates fibrinolysis by limiting the amount of fibrin available for fibrinolysis by tissue plasminogen activator (t-PA). Chronic liver disease is well-known to be associated with a low-grade fibrinolytic syndrome that under the appropriate stimulus proceeds to an overt disseminated intravascular coagulopathy (DIC) with demonstrable bleeding. In the present study, TAFI activity was measured in the plasma of 74 patients with advanced liver disease, and the levels of TAFI were related to those of other important coagulation and fibrinolytic factors. TAFI levels were very low and essentially undetectable in the plasma of patients with advanced hepatocellular liver disease. No relationship with the degradation products of fibrin was evident.

Characterization of thrombin activatable fibrinolysis inhibitor in normal and acquired haemostatic dysfunction.

Thrombin activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase B-like proenzyme, which is synthesized in the liver and circulates in the blood at a concentration of about 275 nmol/l. Once activated, by thrombin or plasmin, TAFI down regulates fibrinolysis, slowing clot lysis by cleaving the C-terminal lysine and arginine residues from partially degraded fibrin. Thrombomodulin enhances thrombin activation of TAFI by more than 1000-fold, suggesting that the thrombin-thrombomodulin complex is the physiological activator of TAFI. Activated protein C can up-regulate fibrinolysis by limiting the activation of TAFI via the attenuation of thrombin production. While impairment of fibrinolysis may predispose to thrombosis, excessive fibrinolysis may result in a bleeding tendency. In acquired coagulopathies, TAFI antigen levels are reduced in patients with disseminated intravascular coagulation. In focusing on women with major post-partum haemorrhage requiring blood transfusion, a significant reduction in TAFI levels is observed. The precise degree of TAFI activation is currently being characterized using new and more specific assays. The resulting data may provide insight into therapeutic options to treat post-partum haemorrhage, which is associated with significant morbidity.

The coagulopathy in acute promyelocytic leukaemia--what have we learned in the past twenty years.

Coagulopathy is a unique component of the pathology of acute promyelocytic leukaemia (APL). Though many causative factors have been elucidated, therapies to rectify the coagulopathy are far from being realised. Thrombotic and bleeding complications remain the major causes of early deaths. In this chapter, the known causes of abnormalities in haemostatic function, namely the coagulopathy and changes in the fibrinolytic system, will be reviewed. Major risk factors for these complications are identified. Current available measures for correction of the coagulopathy and their effectiveness are critically examined. Unless the coagulopathy can be effectively controlled, bleeding complications will remain an obstacle to achieving a cure for this disease. The issues that need to be addressed in next phase of investigations are also discussed.

TAFI deficiency promotes liver damage in murine models of liver failure through defective down-regulation of hepatic inflammation.

Emerging evidence indicates that various haemostatic components can regulate the progression of liver disease. Thrombin-activatable fibrinolysis inhibitor (TAFI) possesses anti-inflammatory properties besides its anti-fibrinolytic function. Here, we investigated the contribution of TAFI to the progression of disease in murine models of chronic and acute liver failure. Chronic carbon tetrachloride (CCL4) administration induced liver damage and fibrosis both in TAFI knockout (TAFI-/-) mice and wild-type controls. Smooth muscle actin-α (α-SMA) content of liver tissue was significantly increased after 1 and 3 weeks, and pro-collagen α1 expression was significantly increased after 3 and 6 weeks in TAFI-/- mice. TAFI-/- mice showed significantly elevated levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) after 3 weeks of CCL4. Neutrophil influx was significantly increased in TAFI-/- mice after 6 weeks of CCL4. No difference in hepatic fibrin deposition between TAFI-/- and wild-types was observed. After acetaminophen intoxication, necrosis was significantly increased in TAFI-/- mice at 24 hours (h) after injection. AST and ALT levels were decreased at 2 and 6 h after acetaminophen injection in TAFI-/- mice, but were significantly higher in the TAFI-/- mice at 24 h. Similarly, hepatic fibrin deposition was decreased at 6 h in TAFI-/- mice, but was comparable to wild-types at 24 h after injection. In conclusion, TAFI deficiency results in accelerated fibrogenesis and increased liver damage in murine models of chronic and acute liver disease, which may be related to increased inflammation.